(1) Field of the Invention
The present invention relates to a process for the preparation of plastic molded articles having a metal film. More particularly, the invention relates to a process for the preparation of plastic molded articles which exhibit a metallic luster and have a thin metal film in the surface layer.
(2) Description of the Prior Art
The optimum method for forming a plastic molded article having a metallic appearance is one comprising forming a metal film on the surface of the molded article. Known conventional methods for forming such a metal film are a vacuum deposition method, a hot stamp method, a plating method and the like.
These conventional methods, however, involve difficulties and problems in connection with the properties of products and the process steps and thus are satisfactory.
For example, in the vacuum deposition method, as described in Japanese Patent Publication No. 39912/78 (Published Unexamined Japanese Patent application No. 138064/75) and Japanese Patent Publication No. 39913/78 (Published Unexamined Japanese Patent application No. 138065/75), only metals having a relatively low melting point, such as aluminum, tin and antimony can be used; it is very difficult to use metals having a high melting point, such as chromium. Moreover, the vacuum deposition method is deficient in that mass production is impossible. Furthermore, the hardness of these low-melting-point metals is low and scratches are readily formed. This in turn readily leads to discoloration, corrosion and elution. Therefore, the vacuum deposition method is not suitable for the purpose of exterior decoration.
The hot stamp method is deficient in that the shape or configuration of plastic molded articles is restricted because of processing limitations.
A strong metal film can be obtained by the plating method, for example, by electrolytic plating with chromium. However, the process steps are complicated and post treatment such as waste water treatment is required. Therefore, this method is deficient from economic and industrial viewpoints.
As a means for eliminating these disadvantages, there has recently been proposed a method in which a film of a metal such as chromium is formed according to a low temperature sputtering process. However, cracks are readily formed in the metal film during the film-forming process or during use, the decorative appearance is markedly degraded and the formed metal film readily peels from the coating. Accordingly, even this method has not been put into practical use.